Within the area of wind turbine construction and operation, it is well known that a reliable and versatile control system is needed in order to achieve the desired function and energy output from the wind turbine while at the same time creating a safe and reliable environment in the vicinity of the wind turbine itself, where the risk of damages to the machinery and the surrounding area can be avoided.
While in operation, many kinds of control system for controlling the pitch of the turbine blades and for keeping the output from the wind turbine system at a desired level are known. However, there is also a need for an emergency system for stopping the turbine altogether if an unexpected event such as a power failure in the control system should occur.
A control system for controlling the pitch angles of turbine blades on a wind turbine is shown in U.S. Pat. No. 5,226,805, where the turbine blades are resiliently biased towards a rest position, using coiled springs to automatically vary the pitch angles of the turbine blades in response to variations in the wind speed and the load. This system allows for a convenient, low-tech control over the speed of the turbine in order to determine the desired output from the wind turbine. There is, however, no possibility at all for emergency shut-down of the system, which is a major disadvantage.
Another device for controlling the pitch angle of wind turbine blades is shown in DE 42 21 783, where an electrical motor rotates together with the main shaft of a wind turbine. The motor adjusts the pitch angle of the blades, but the system has no way of stopping the rotation of the wind turbine in the event of a power failure to the control system, since a disruption in the power supply to the control system would also disrupt the operation of the electrical motor itself.
A device for adjusting the pitch and stopping the rotation of the blades of a wind turbine is shown by U.S. Pat. No. 6,609,889 (Vilsboll), where a separate brake is added for braking the rotation of the turbine. This device is, however, dependent on a motor for altering the pitch of the turbine blades, and in the event of a malfunction of this motor or a loss of energy in the system, a situation might arise where the turbine itself is halted but the turbine blades are still pitched to an operating position. In this event, a considerable load is added to the wind turbine by the force of the wind on the turbine blades without the turbine itself being able to rotate, and this would create a considerable risk for damages to the entire wind turbine.
Another device for altering the pitch of turbine blades of a wind turbine is shown by U.S. Pat. No. 5,779,446 (Althof et al.), where a separate pitch motor is required for altering the pitch of the blades. This device is also at risk for serious damages in the event of a sudden power loss, since the pitch of the turbine blades cannot in this event be pitched to feather in a safe way, in order to minimize air resistance.
There is therefore a need for a wind turbine with a control system that has a mechanism for emergency braking in a reliable and efficient manner.